# Difference between float and double in C/C++

For representing floating point numbers, we use float, double and long double.

What’s the difference ?

double has 2x more precision then float.

float is a 32 bit IEEE 754 single precision Floating Point Number1 bit for the sign, (8 bits for the exponent, and 23* for the value), i.e. float has 7 decimal digits of precision.

double is a 64 bit IEEE 754 double precision Floating Point Number (1 bit for the sign, 11 bits for the exponent, and 52* bits for the value), i.e. double has 15 decimal digits of precision.

Let’s take a example(example taken from here) :
For a quadratic equation x2 – 4.0000000 x + 3.9999999 = 0, the exact roots to 10 significant digits are, r1 = 2.000316228 and r2 = 1.999683772

 // C program to demonstrate  // double and float precision values    #include #include    // utility function which calculate roots of  // quadratic equation using double values void double_solve(double a, double b, double c){     double d = b*b - 4.0*a*c;     double sd = sqrt(d);     double r1 = (-b + sd) / (2.0*a);     double r2 = (-b - sd) / (2.0*a);     printf("%.5f %.5f ", r1, r2); }    // utility function which calculate roots of  // quadratic equation using float values void float_solve(float a, float b, float c){     float d = b*b - 4.0f*a*c;     float sd = sqrtf(d);     float r1 = (-b + sd) / (2.0f*a);     float r2 = (-b - sd) / (2.0f*a);     printf("%.5f %.5f ", r1, r2); }       // driver program int main(){     float fa = 1.0f;     float fb = -4.0000000f;     float fc = 3.9999999f;     double da = 1.0;     double db = -4.0000000;     double dc = 3.9999999;        printf("roots of equation x2 - 4.0000000 x + 3.9999999 = 0 are : ");     printf("for float values: ");     float_solve(fa, fb, fc);        printf("for double values: ");     double_solve(da, db, dc);     return 0; }

/div>

Output:

roots of equation x2 - 4.0000000 x + 3.9999999 = 0 are :
for float values:
2.00000    2.00000
for double values:
2.00032    1.99968

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## tags:

C Difference Between cpp-data-types C